Networks for mobile telecommunications terminals are known in the prior art. These networks are in general referred to as cellular inasmuch as they are characterized by a plurality of cells, each defined as the set of points or pixels in the geographical area which are served by the radioelectric signal radiated by an antenna.
Among known cellular networks, those which use the CDMA access technique are distinguished by the fact that the same frequency band (channel) can be used in different cells. As a result, handover, or in other words the techniques employed when a mobile terminal moves from one cell to another adjacent cell, can be managed by using the same frequency. Such techniques are called soft handover, which is a mechanism that enables the mobile terminal to decode signals when it is located in certain areas referred to as soft handover or macrodiversity areas, and thus exchange information with several antennas and, consequently, several radio base stations (RBSs). Naturally, identifying and dimensioning the macrodiversity areas is extremely important as regards the correct operation and dimensioning of cell equipment, since a mobile terminal implementing the macrodiversity mechanism will obviously use resources from all of the radio base stations to which it is simultaneously connected.
A further distinguishing feature of UMTS networks consists in the fact that these networks are capable of providing a plurality of “services”, examples of which include:                Telephony        Fax        Video telephony        Internet access        
In general, moreover, each of these services has characteristics in terms of speed (bit rate) and traffic (quantity and whether the traffic is symmetrical or asymmetrical) which are specific for the service concerned. It follows that the factors to be taken into account when dimensioning cells include both the characteristics of each service, and any groupings of services on a single radio carrier as envisaged by the CDMA access technique. Like all cellular mobile radio systems, UMTS features common control channels that are broadcast over the entire cell area. These channels contain system information which is indispensable for the mobile terminals. Because of these particular characteristics, UMTS network planning is thus a complex activity that calls for approaches differing substantially from those hitherto used for earlier types of cellular network such as GSM (Global System for Mobile Communication) or IS-95 (Interim Standard).
There are a number of prior-art systems and methods for planning mobile terminal networks which use the CDMA access technique. For example, the document AC016/CSE/MRM/DR/P/091/al entitled “STORMS Project Final Report” describes the system and method developed as part of the STORMS project (Software Tools for the Optimization of Resources in Mobile Systems) promoted by the European Commission.
The prior-art method and system are characterized by three main steps:
A first step 10 (FIG. 1) called “Initial Dimensioning” consists of calculating maximum cell dimensions on the basis of theoretical propagation models for any given service. For calculation in this step 10, cells are by convention considered to be hexagonal and traffic is considered to be uniformly distributed over the geographical area concerned.
A second step 20, called “Radio Coverage Optimization”, consists of calculating the dimensions of the cells′ so-called “service area” for any given service or for mixed services, taking the specific propagation models for the geographical area concerned into account. In this step 20, calculation considers that the cells are mutually exclusive and that there are thus no geographical areas (pixels) implementing macrodiversity.
A third step 30, called “Fine Cell Dimensioning”, is designed to calculate the actual dimensions of the cells for any given service or for mixed services in cases where a single carrier is used for multiple services. In this step, both propagation and the actual traffic in the geographical area are taken into account, as is the effect of the power control function.
In this final step 30, calculation is performed through successive approximations and leads to a real network plan.
On the whole, the prior art method is very slow to converge on a real network plan because of the approximations introduced in the first two calculation steps (10 and 20), which mean that the third step is invariably necessary. Consequently, the prior art method is actually usable only at the end of the planning process, since all of the parameters required for correct network planning are taken into consideration only in the final step 30.
In addition, the prior art method is not capable of providing information about the dimensions of the macrodiversity areas, even though these areas are particularly critical because they make it necessary to use an amount of network equipment in excess of that required by the actual traffic density, given that the mobile terminals in these areas communicate with several units simultaneously.
Essentially, the prior art method and system, though providing a solution to the problem of dimensioning networks using the CDMA access technique, are slow, fail to furnish realistic intermediate results, and neglect macrodiversity, which is one of the factors that is most difficult to manage for any operator who intends to provide third-generation network services.